
package org.apache.ibatis.ibator.internal.util;

import java.lang.reflect.Array;

/**
 * This class is from javapractices.com:
 * http://www.javapractices.com/Topic28.cjp Collected methods which allow easy
 * implementation of <code>hashCode</code>. Example use case:
 * 
 * <pre>
 * public int hashCode()
 * {
 * 	int result = HashCodeUtil.SEED;
 * 	// collect the contributions of various fields
 * 	result = HashCodeUtil.hash(result, fPrimitive);
 * 	result = HashCodeUtil.hash(result, fObject);
 * 	result = HashCodeUtil.hash(result, fArray);
 * 	return result;
 * }
 * </pre>
 */
public final class HashCodeUtil
{

	/**
	 * An initial value for a <code>hashCode</code>, to which is added
	 * contributions from fields. Using a non-zero value decreases collisons of
	 * <code>hashCode</code> values.
	 */
	public static final int SEED = 23;

	/**
	 * booleans.
	 */
	public static int hash(int aSeed, boolean aBoolean)
	{
		return firstTerm(aSeed) + (aBoolean ? 1 : 0);
	}

	/**
	 * chars.
	 */
	public static int hash(int aSeed, char aChar)
	{
		return firstTerm(aSeed) + aChar;
	}

	/**
	 * ints.
	 */
	public static int hash(int aSeed, int aInt)
	{
		/*
		 * Implementation Note Note that byte and short are handled by this
		 * method, through implicit conversion.
		 */
		return firstTerm(aSeed) + aInt;
	}

	/**
	 * longs.
	 */
	public static int hash(int aSeed, long aLong)
	{
		return firstTerm(aSeed) + (int) (aLong ^ (aLong >>> 32));
	}

	/**
	 * floats.
	 */
	public static int hash(int aSeed, float aFloat)
	{
		return hash(aSeed, Float.floatToIntBits(aFloat));
	}

	/**
	 * doubles.
	 */
	public static int hash(int aSeed, double aDouble)
	{
		return hash(aSeed, Double.doubleToLongBits(aDouble));
	}

	/**
	 * <code>aObject</code> is a possibly-null object field, and possibly an
	 * array. If <code>aObject</code> is an array, then each element may be a
	 * primitive or a possibly-null object.
	 */
	public static int hash(int aSeed, Object aObject)
	{
		int result = aSeed;
		if (aObject == null)
		{
			result = hash(result, 0);
		}
		else
			if (!isArray(aObject))
			{
				result = hash(result, aObject.hashCode());
			}
			else
			{
				int length = Array.getLength(aObject);
				for (int idx = 0; idx < length; ++idx)
				{
					Object item = Array.get(aObject, idx);
					// recursive call!
					result = hash(result, item);
				}
			}
		return result;
	}

	// / PRIVATE ///
	private static final int fODD_PRIME_NUMBER = 37;

	private static int firstTerm(int aSeed)
	{
		return fODD_PRIME_NUMBER * aSeed;
	}

	private static boolean isArray(Object aObject)
	{
		return aObject.getClass().isArray();
	}
}
